1. Field of the Invention
The present invention relates to an evaluation signal forming apparatus suitable for a reproduce drive device in respect of various record media, and a focus bias adjusting method and a skew adjusting method suitable for a drive device in respect of a disk-like record medium.
2. Description of Related Art
CD (Compact Disk) has widely been spread as an optical disk record medium and a disk of CD style is used in various fields including musical usage. Further, a disk referred to as DVD (Digital Versatile Disk/Digital Video Disk) has been developed as an optical disk record medium suitable for multi media usage. DVD is proposed to be adaptable to wide fields of video data, audio data, computer data and the like. Although DVD is a disk (diameter 12 cm) having a size the same as that of CD, the record capacity is remarkably increased by small pitch formation of record track, data compression technology and the like.
Meanwhile, in respect of a reproduce drive device for a record medium of CD, DVD or the like, as a method of evaluating quality of reproduce signal, there is a method of evaluating a jitter component between a signal read from a disk and binarized (for example, EFM signal in CD) and a clock formed by inputting the binarized signal to a PLL circuit (that is, reproduce clock in synchronism with reproduce signal), or the like.
The jitter component is detected as a dispersion or a standard deviation shown by the following Equation (1) and Equation (2) with respect to a phase error between a phase of a binarized signal and a phase of the reproduce clock.                               ∑          i                ⁢                              (                          Xi              -                              X                AVG                                      )                    2                                    (        1        )                                                      ∑            i                    ⁢                                    (                              Xi                -                                  X                  AVG                                            )                        2                                              (        2        )            
where Xi is a value of phase error and XAVG is average value.
FIGS. 1A, 1B, 1C and 1D show an example of an operation for detecting a phase error between a phase of a binarized signal and a phase of a reproduce clock. FIG. 1A indicates a reproduce clock PLCK formed by inputting an EFM signal that is a binarized signal to a PLL circuit and FIG. 13B indicates the EFM signal (8-14 modulated signal). Further, an EFMO signal in FIG. 1C, is a signal formed by supplying the EFM signal to latching means such as a flip flop circuit or the like and latching it at an edge timing of the reproduce clock PLCK.
Incidentally, arising edge of a waveform is referred to as xe2x80x9cedgexe2x80x9d and a falling edge of a waveform is referred to as xe2x80x9ccounter edgexe2x80x9d for convenience of explanation in the specification.
FIG. 1D indicates a phase error signal PDO and the phase error signal PDO corresponds to a signal showing a time period from an edge of the EFM signal to an edge of the reproduce clock PLCK.
A very large-scaled device such as TIA (Time Interval Analyzer) is needed to calculate standard deviation or dispersion used for signal evaluation from such a phase error signal PDO.
There are focus bias or skew state as factors influencing on the quality of a reproduce signal in a disk drive device. It is preferable to perform adjusting operation to optimize these values while detecting a value in correspondence with a jitter component. However, it is preferable to execute such an adjustment not only in an adjusting step before shipment in a factory but in actually using a disk drive device, for example, at every time of loading a disk. That is, an optimum value (state) for adjusting focus bias or skew are varied by environmental state of using the disk drive device such as temperature or the like, aging change, difference in mechanical/optical properties for individual disks and the like.
However, it is not realistic to mount TIA or the like having a large circuit constitution on a disk drive device in consideration of size and cost of the device. Therefore, it is difficult to adjust focus bias or skew initial state by automatically performing signal evaluation by detecting jitter in, for example, inserting a disk in a disk drive device.
As a method of substituting for signal evaluation using standard deviation, there is a method where an absolute value of the phase error signal PDO is used. That is, the valued is derived from Equation (3).                               ∑          i                ⁢                  "LeftBracketingBar"                      Xi            -                          X              AVG                                "RightBracketingBar"                                    (        3        )            
However, in order to determine the absolute value as an evaluation value for various adjustments a signal in accordance with the absolute value must be converted into a numerical value. That is, the pulse width of the phase error signal PDO in FIG. 1D is converted into a numerical value. For that purpose, a clock having high frequency for sampling and measuring the phase error signal PDO, becomes necessary. For example, a clock formed by multiplying a reproduce clock by n or the like is needed.
However, such a clock is difficult to realize since with high transmission rate formation of reproduce data of a disk drive device in recent years, the frequency per se of a reproduce signal from a disk becomes higher and accordingly, the frequency of the clock for measuring the absolute value of the phase error becomes higher.
It is an object of the present invention in view of such a problem to provide an adjusting method capable of forming and detecting an evaluation signal capable of constituting an evaluation reference of quality of signals by a simple constitution and using the evaluation signal.
For that purpose, an evaluation signal forming apparatus is constituted by phase error detecting means for detecting phase error information between a phase of a read data signal read from a record medium and a clock signal formed in synchronism with the read data signal, and outputting means for outputting an evaluation signal having a signal level in correspondence with the phase error information.
That is, phase error information is not sampled as it is but is converted into an analog signal having the signal level in accordance with the phase error information. Further, when the analog signal is determined as the evaluation signal, a portion (for example, microcomputer) for carrying out signal quality evaluation by using the evaluation signal, takes in the evaluation signal by A/D-converting the evaluation signal.
Further, the focus bias value is varied while monitoring such an evaluation signal and the focus bias value at a time point where the value of the evaluation signal becomes a pertinent value, is set as an adjustment value of the focus bias value.
Also, skew driving is carried out while monitoring the evaluation signal and a skew state at a time point when the value of the evaluation signal becomes a pertinent value, is set as an optimum skew initial state.
Accordingly, by realizing accurate signal evaluation by a simple constitution, the focus bias adjustment, skew initial state adjustment and the like can be automated by a unit of the drive device.